An electronic component such as SAW filter and crystal oscillator employed in an electronic device such as mobile phone is used as a package fabricated by housing such an electronic component in a case with an opening and sealing the case by putting a lid thereon. The package is sealed so as to prevent the properties of the electronic component from becoming unstable due to moisture or oxygen in the air.
In this electronic component package, the case is generally made of ceramic such as alumina and aluminum nitride, and the lid is composed of a low thermal expansion metal such as KOVAR (iron-nickel-cobalt alloy, U.S. Registered Trademark Serial No. 71367381) and iron-nickel alloy.
The method for joining the lid to the case includes a method of achieving the joining by use of a clad material obtained by previously bonding a brazing material to a base material that works out to a lid (see, for example, Patent Document 1). Apart from this, there is also a method of providing, on the above-described ceramic-made case, a frame-shaped seal ring composed of a metal such as KOVAR clad with a brazing material, and joining a lid to the top surface of the seal ring (see, for example, Patent Document 2).
FIG. 4 is a diagram for explaining the method for joining a lid to a case housed therein an electronic component by using a seal ring.
In FIG. 4, (1) KOVAR 402 and a metal brazing material 404 are prepared, (2) these are laminated together to form a clad material 40, (3) the clad material is processed by rolling, (4) the rolled clad material 40 is pressed into a ring shape, (5) a ceramic-made case 46 having housed therein an electronic component is prepared, (6) the metal brazing material 404 and the case 46 are seam-welded to come into contact with each other, (7) a metal layer 48 such as nickel or gold is provided on the top surface of KOVAR 402 of the seal ring, and (8) a lid 49 is joined to the top of the metal layer 48.
However, when a conventional seal ring is used, a phenomenon of generation of a stain on the top surface of the metal layer 48 is observed. FIG. 5(a) is a plan view illustrating two stains generated on the conventional metal layer 48, and FIG. 5(b) is an enlarged photograph thereof. The stain illustrated in FIGS. 5(a) and 5(b) corresponds to a void of the metal layer 48 and causes a serious problem of deterioration of the airtightness between the seal ring and the lid 49.